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We present a continuous ostracod isotope (delta O-18 and delta C-13) record from Lake Peten Itza, Peten, Guatemala, in the northern, lowland Neotropics that spans the last similar to 43 cal ka BR Variations in oxygen and carbon isotopes closely follow lithologic variations, which consist of alternating gypsum and clay deposits that were deposited under relatively dry and wet climate, respectively. During the last glacial period, the greatest delta O-18 and delta C-13 values coincide with gypsum deposited during lake lowstands under arid climate conditions that were correlated previously with North Atlantic Heinrich events. In contrast, interstadials and the entirety of the Last Glacial Maximum (similar to 24-19 cal ka BP) are marked by clay deposition and lower delta O-18 and delta C-13 values, reflecting higher lake levels and relatively moister climate.

Isotope results and pollen data, along with independently inferred past water levels, show the early deglacial period (similar to 19-15 cal ka BP) was the time of greatest aridity and lowest lake stage of the past 43 ka. This period occurred during Heinrich Stadial 1 (HS 1), when an extensive tropical megadrought has been postulated (Stager et al., 2011). Heinrich Stadial 1 is represented by two episodes of gypsum precipitation and high delta O-18 and delta C-13 values in Peten Itza, interrupted by an intervening period of lower delta O-18 and delta C-13 and clay deposition centered on similar to 17 cal ka BR The two periods of inferred maximum cold and/or arid conditions at similar to 17.5 and 16.1 cal ka BP coincide approximately with two pulses of ice-rafted debris (IRD) recorded off southern Portugal (Bard et al., 2000). At similar to 15 cal ka BP, coinciding with the start of the Bolling-Allerod period, delta O-18 and delta C-13 decrease and gypsum precipitation ceases, indicating a transition to warmer and/or wetter conditions. Gypsum precipitation resumed while delta O-18 and delta C-13 increased at the start of the Younger Dryas at 13.1 cal ka BP and continued until 10.4 cal ka BP, near the onset of the Holocene.

Precipitation changes during the last glacial period in the northern hemisphere Neotropics were closely linked with freshwater forcing to the high-latitude North Atlantic, and sensitive to changes in the location of meltwater input. Climate was coldest/driest when meltwater directly entered the high-latitude North Atlantic, permitting sea ice expansion and weakening of Atlantic Meridional Overturning Circulation (AMOC), which resulted in a more southerly position of the Intertropical Convergence Zone (ITCZ). Upon deglaciation, when meltwater was directed to the Gulf of Mexico, at similar to 17 ka and during the Bolling-Allerod period (15-13 ka), precipitation increased in the northern hemisphere Neotropics as North Atlantic sea ice retreated and the ITCZ shifted northward. Results from Lake Peten Itza offer some support for the meltwater routing hypothesis of Clark et al. (2001). (C) 2012 Elsevier Ltd. All rights reserved.